/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.dx.util;

import java.io.UTFDataFormatException;

/**
 * Modified UTF-8 as described in the dex file format spec.
 * <p>
 * Derived from libcore's MUTF-8 encoder at java.nio.charset.ModifiedUtf8.
 */
public final class Mutf8 {

	private Mutf8() {
	}

	/**
	 * Decodes bytes from {@code in} into {@code out} until a delimiter 0x00 is
	 * encountered. Returns a new string containing the decoded characters.
	 */
	public static String decode(ByteInput in, char[] out)
			throws UTFDataFormatException {
		int s = 0;
		while (true) {
			char a = (char) (in.readByte() & 0xff);
			if (a == 0) {
				return new String(out, 0, s);
			}
			out[s] = a;
			if (a < '\u0080') {
				s++;
			} else if ((a & 0xe0) == 0xc0) {
				int b = in.readByte() & 0xff;
				if ((b & 0xC0) != 0x80) {
					throw new UTFDataFormatException("bad second byte");
				}
				out[s++] = (char) (((a & 0x1F) << 6) | (b & 0x3F));
			} else if ((a & 0xf0) == 0xe0) {
				int b = in.readByte() & 0xff;
				int c = in.readByte() & 0xff;
				if (((b & 0xC0) != 0x80) || ((c & 0xC0) != 0x80)) {
					throw new UTFDataFormatException("bad second or third byte");
				}
				out[s++] = (char) (((a & 0x0F) << 12) | ((b & 0x3F) << 6) | (c & 0x3F));
			} else {
				throw new UTFDataFormatException("bad byte");
			}
		}
	}

	/**
	 * Returns the number of bytes the modified UTF8 representation of 's' would
	 * take.
	 */
	private static long countBytes(String s, boolean shortLength)
			throws UTFDataFormatException {
		long result = 0;
		final int length = s.length();
		for (int i = 0; i < length; ++i) {
			char ch = s.charAt(i);
			if (ch != 0 && ch <= 127) { // U+0000 uses two bytes.
				++result;
			} else if (ch <= 2047) {
				result += 2;
			} else {
				result += 3;
			}
			if (shortLength && result > 65535) {
				throw new UTFDataFormatException(
						"String more than 65535 UTF bytes long");
			}
		}
		return result;
	}

	/**
	 * Encodes the modified UTF-8 bytes corresponding to {@code s} into
	 * {@code dst}, starting at {@code offset}.
	 */
	public static void encode(byte[] dst, int offset, String s) {
		final int length = s.length();
		for (int i = 0; i < length; i++) {
			char ch = s.charAt(i);
			if (ch != 0 && ch <= 127) { // U+0000 uses two bytes.
				dst[offset++] = (byte) ch;
			} else if (ch <= 2047) {
				dst[offset++] = (byte) (0xc0 | (0x1f & (ch >> 6)));
				dst[offset++] = (byte) (0x80 | (0x3f & ch));
			} else {
				dst[offset++] = (byte) (0xe0 | (0x0f & (ch >> 12)));
				dst[offset++] = (byte) (0x80 | (0x3f & (ch >> 6)));
				dst[offset++] = (byte) (0x80 | (0x3f & ch));
			}
		}
	}

	/**
	 * Returns an array containing the <i>modified UTF-8</i> form of {@code s}.
	 */
	public static byte[] encode(String s) throws UTFDataFormatException {
		int utfCount = (int) countBytes(s, true);
		byte[] result = new byte[utfCount];
		encode(result, 0, s);
		return result;
	}
}
